1. Field
The present teachings relate to sensing current. In particular, the present teachings relate to current sensing at diverse locations in an extended area such as a substrate of an integrated circuit.
2. Background
Current sensing can be carried out in a variety of ways. In a first approach, the current is propagated through a resistor having a known resistance value and the resulting voltage drop across the resistor is measured in order to determine the amplitude of the current flowing through the resistor. As can be appreciated this approach involves undesirable power wastage in the resistor, thereby leading to a reduction in the overall amount of power that can be provided to a load circuit through the resistor.
In a second approach, an operational amplifier is configured to generate a sense signal that is proportional to the value of a current flowing through a current carrying line. While the operational amplifier approach addresses the undesired output power reduction problem associated with a current sensing resistor, this second approach also suffers from several shortcomings.
Among the several shortcomings, one pertains to bandwidth. Typically, the bandwidth of an operational amplifier (especially one that is configured as a gain element incorporating a feedback circuit) has to be several orders higher than the bandwidth of an AC input signal provided to the operational amplifier. For example, if the frequency of the AC signal provided to the non-inverting terminal of an operational amplifier is around 25 MHz, the operational amplifier has to be selected to have a bandwidth of around 250 MHz (i.e., a decade multiple of the input AC frequency). This large bandwidth requirement places an undesirable limitation on the type of operational amplifier that can be used in various applications such as current sensing, consequently curtailing choices of operational amplifiers to a limited sub-set of devices amongst a plurality of available devices.
Furthermore, the large bandwidth can not only lead to unstable circuit performance (especially when the gain of the circuit is increased beyond a certain level) but also necessitates careful circuit design as well as component layout.
To elaborate upon the component layout issue, it can be understood that an operational amplifier circuit typically involves routing analog signals among various components. Several factors come into play when the circuit is active, especially when the analog signals are high frequency analog signals. These factors include, for example, cross-talk, signal-to-noise degradation, signal attenuation, and signal distortion.
Consequently, all such factors have to be taken into consideration during circuit layout when the various components of an analog circuit are laid out over an extended area, such as, for example, a substrate contained inside an integrated circuit. This task is further compounded when a plurality of identical circuits are to be laid out over a substrate and various signals that are somewhat similar in nature can interact with each other in an adverse manner.